Malignant tumors (cancers) are the second leading cause of death in the United States, after heart disease. Boring et al., CA Cancer J. Clin., 43: 7 (1993).
Cancer is characterized by the increase in the number of abnormal, or neoplastic, cells derived from a normal tissue which proliferate to form a tumor mass, the invasion of adjacent tissues by these neoplastic tumor cells, and the generation of malignant cells which eventually spread via the blood or lymphatic system to regional lymph nodes and to distant sites (metastasis). In a cancerous state a cell proliferates under conditions in which normal cells would not grow. Cancer manifests itself in a wide variety of forms, characterized by different degrees of invasiveness and aggressiveness.
Alteration of gene expression is intimately related to the uncontrolled cell growth and de-differentiation which are a common feature of all cancers. The genomes of certain well studied tumors have been found to show decreased expression of recessive genes, usually referred to as tumor suppression genes, which would normally function to prevent malignant cell growth, and/or overexpression of certain dominant genes, such as oncogenes, that act to promote malignant growth. Each of these genetic changes appears to be responsible for importing some of the traits that, in aggregate, represent the full neoplastic phenotype. Hunter, Cell, 64: 1129 (1991); Bishop, Cell, 64: 235–248 (1991).
A well-known mechanism of gene (e.g., oncogene) overexpression in cancer cells is gene amplification. This is a process where in the chromosome of the ancestral cell multiple copies of a particular gene are produced. The process involves unscheduled replication of the region of chromosome comprising the gene, followed by recombination of the replicated segments back into the chromosome. Alitalo et al., Adv. Cancer Res., 47: 235–281 (1986). It is believed that the overexpression of the gene parallels gene amplification, i.e., is proportionate to the number of copies made.
Proto-oncogenes that encode growth factors and growth factor receptors have been identified to play important roles in the pathogenesis of various human malignancies, including breast cancer. For example, it has been found that the human ErbB2 gene (erbB2, also known as her2, or c-erbB-2), which encodes a 185-kd transmembrane glycoprotein receptor (p185HER2; HER2) related to the epidermal growth factor receptor (EGFR), is overexpressed in about 25% to 30% of human breast cancer. Slamon et al., Science, 235:177–182 (1987); Slamon et al., Science, 244:707–712 (1989). It has been reported that gene amplification of a protooncogen is an event typically involved in the more malignant forms of cancer, and could act as a predictor of clinical outcome. Schwab et al., Genes Chromosomes Cancer, 1: 181–193 (1990); Alitalo et al., supra. Thus, erbB2 overexpression is commonly regarded as a predictor of a poor prognosis, especially in patients with primary disease that involves axillary lymph nodes (Slamon et al., (1987) and (1989), supra; Ravdin and Chamness, Gene, 159:19–27 (1995); and Hynes and Stern, Biochim Biophys Acta, 1198:165–184 (1994)), and has been linked to sensitivity and/or resistance to hormone therapy and chemotherapeutic regimens, including CMF (cyclophosphamide, methotrexate, and fluoruracil) and anthracyclines. Baselga et al., Oncology, 11(3 Suppl 1):43–48 (1997). However, despite the association of erbB2 overexpression with poor prognosis, the odds of HER2-positive patients responding clinically to treatment with taxanes were greater than three times those of HER2-negative patients. Baselga et al., supra. A recombinant humanized anti-ErbB2 (anti-HER2) monoclonal antibody (a humanized version of the murine anti-ErbB2 antibody 4D5, referred to as rhuMAb HER2 or HERCEPTIN®) has been clinically active in patients with ErbB2-overexpressing metastatic breast cancers that had received extensive prior anticancer therapy. Baselga et al., J. Clin. Oncol., 14:737–744 (1996).
Cytokines have been implicated in the pathogenesis of a number of brain diseases in which neurological dysfunction has been attributed to a change in amino acid neurotransmitter metabolism. In particular, members of the transforming growth factor-β (TGF-β) family have been implicated. TGF peptides are small polypeptides that were first identified by their ability to induce proliferation and transformation in noncancerous cells in culture. Although initially defined as a growth factor, TGF-β also inhibits proliferation of epithelial, endothelial, lymphoid, and hematopoietic cells. This cytokine is thought to play an important role in regulating the duration of the inflammatory response, allowing the healing process to proceed. It is also a potent immunomodulator, which has many pleiotrophic effects, including regulating many other cytokines.
The TGF-β superfamily includes bone morphogenetic proteins (BMP-2, BMP-4, BMP-5, BMP-6, BMP-7), activins A & B, decapentaplegic (dpp), 60A, OP-2, dorsalin, growth differentiation factors (GDFs), nodal, MIS, Inhibin-α, TGF-β1, TGF-β2, TGF-β3, TGF-β5, and glial-derived neurotrophic factor (GDNF). Atrisano, et al., J. Biochemica et Biophysica Acta, 1222:71–80 (1994). Of particular interest are the growth differentiation factors, for as their name implies, these factors are implicated in the differentiation of cells.
Connective tissue growth factor (CTGF) is a growth factor induced in fibroblasts by many factors, including TGF-β, and is essential for the ability of TGF-β to induce anchorage-independent growth (AIG), a property of transformed cells. CTGF was discovered in an attempt to identify the type of platelet-derived growth factor (PDGF) dimers present in the growth media of cultured endothelial cells, and is related immunologically and biologically to PDGF. See U.S. Pat. No. 5,408,040. CTGF also is mitogenic and chemotactic for cells, and hence growth factors in this family are believed to play a role in the normal development, growth, and repair of human tissue.
Seven proteins related to CTGF, including the chicken ortholog for Cyr61, CEF10, human, mouse, and Xenopus laevis CTGF, and human, chicken, and Xenopus laevis Nov have been isolated, cloned, sequenced, and characterized as belonging to the CTGF gene family. Oemar and Luescher, Arterioscler. Thromb. Vasc. Biol., 17: 1483–1489 (1997). The gene encoding Cyr61 has been found to promote angiogenesis, tumor growth, and vascularization. Babic et al., Proc. Natl. Acad. Sci. USA, 95: 6355–6360 (1998). The nov gene is expressed in the kidney essentially at the embryonic stage, and alterations of nov expression, relative to the normal kidney, have been detected in both avian nephroblastomas and human Wilms' tumors. Martinerie et al., Oncogene, 9: 2729–2732 (1994). Wt1 downregulates human nov expression, which downregulation might represent a key element in normal and tumoral nephrogenesis. Martinerie et al., Oncogene, 12: 1479–1492 (1996). It has recently been proposed that the CTGF, nov, and cyr61 genes, which encode secreted proteins that contain conserved sequences and IGFBP motifs in their N-termini and bind IGFs with low affinity, represent more members of the IGFBP superfamily, along with the low-affinity mac25/IGFBP-7 (Yamanaka et al., J. Biol. Chem., 272: 30729–30734 (1997)) and the high-affinity IGFBPs 1–6. CTGF under this proposal would be designated IGFBP-8. Kim et al., Proc. Natl. Acad. Sci. USA, 94: 12981–12986 (1997).
Recently, a protein was found in the mouse designated ELM1 that is expressed in low metastatic cells. Hashimoto et al., J. Exp. Med., 187: 289–296 (1998). The elm1 gene, a mouse homologue of WISP-1 disclosed below, is another member of the CTGF, Cyr61/Cef10, and neuroblastoma overexpressed-gene family and suppresses in vivo tumor growth and metastasis of K-1735 murine melanoma cells. Another recent article on rCop-1, the rat orthologue of WISP-2 described below describes the loss of expression of this gene after cell transformation. Zhang et al., Mol. Cell. Biol., 18:6131–6141 (1998).
CTGF family members (with the exception of nov) are immediate early growth-responsive genes that are thought to regulate cell proliferation, differentiation, embryogenesis, and wound healing. Sequence homology among members of the CTGF gene family is high; however, functions of these proteins in vitro range from growth stimulatory (i.e., human CTGF) to growth inhibitory (i.e., chicken Nov and also possibly hCTGF). Further, some molecules homologous to CTGF are indicated to be useful in the prevention of desmoplasia, the formation of highly cellular, excessive connective tissue stroma associated with some cancers, and fibrotic lesions associated with various skin disorders such as scleroderma, keloid, eosinophilic fasciitis, nodular fasciitis, and Dupuytren's contracture. Moreover, CTGF expression has recently been demonstrated in the fibrous stoma of mammary tumors, suggesting cancer stroma formation involves the induction of similar fibroproliferative growth factors as wound repair. Human CTGF is also expressed at very high levels in advanced atherosclerotic lesions, but not in normal arteries, suggesting it may play a role in atherosclerosis. Oemar and Luescher, supra. Therefore, molecules homologous to CTGF are of importance.
Extracellular and membrane-bound proteins play important roles in the formation, differentiation, and maintenance of multicellular organisms. The fate of many individual cells, e.g., proliferation, migration, differentiation, or interaction with other cells, is typically governed by information received from other cells and/or the immediate environment. This information is often transmitted by secreted polypeptides (for instance, mitogenic factors, survival factors, cytotoxic factors, differentiation factors, neuropeptides, and hormones), which are, in turn, received and interpreted by diverse cell receptors or membrane-bound proteins. These secreted polypeptides or signaling molecules normally pass through the cellular secretory pathway to reach their site of action in the extracellular environment, usually at a membrane-bound receptor protein.
Secreted proteins have various industrial applications, including use as pharmaceuticals, diagnostics, biosensors, and bioreactors. In fact, most protein drugs available at present, such as thrombolytic agents, interferons, interleukins, erythropoietins, colony stimulating factors, and various other cytokines, are secreted proteins. Their receptors, which are membrane-bound proteins, also have potential as therapeutic or diagnostic agents. Receptor immunoadhesins, for instance, can be employed as therapeutic agents to block receptor-ligand interaction. Membrane-bound proteins can also be employed for screening of potential peptide or small molecule inhibitors of the relevant recoptor/ligand interaction. Such membrane-bound proteins and cell receptors include, but are not limited to, cytokine receptors, receptor kinases, receptor phosphatases, receptors involved in cell-cell interactions, and cellular adhesin molecules like selectins and integrins. Transduction of signals that regulate cell growth and differentiation is regulated in part by phosphorylation of various cellular proteins. Protein tyrosine kinases, enzymes that catalyze that process, can also act as growth factor receptors. Examples include fibroblast growth factor receptor and nerve growth factor receptor.
Efforts are being undertaken by both industry and academia to identify new, native secreted and membrane-bound receptor proteins, particularly those having homology to CTGF. Many efforts are focused on the screening of mammalian recombinant DNA libraries to identify the coding sequences for novel secreted and membrane-bound receptor proteins. Examples of screening methods and techniques are described in the literature. See, for example, Klein et al., Proc. Natl. Acad. Sci., 93:7108–7113 (1996); and U.S. Pat. No. 5,536,637.
Wnts are encoded by a large gene family whose members have been found in round worms, insects, cartilaginous fish, and vertebrates. Holland et al., Dev. Suppl., 125–133 (1994). Wnts are thought to function in a variety of developmental and physiological processes since many diverse species have multiple conserved Wnt genes. McMahon, Trends Genet., 8: 236–242 (1992); Nusse and Varmus, Cell, 69: 1073–1087 (1992). Wnt genes encode secreted glycoproteins that are thought to function as paracrine or autocrine signals active in several primitive cell types. McMahon, supra (1992); Nusse and Varmus, supra (1992). The Wnt growth factor family includes more than ten genes identified in the mouse (Wnt-1, -2, -3A, -3B, -4, -5A, -5B, -6, -7A, -7B, -8A, -8B, -10B, -11, -12, and -13) (see, e.g., Gavin et al., Genes Dev., 4: 2319–2332 (1990); Lee et al., Proc. Natl. Acad. Sci. USA, 92: 2268–2272 (1995); Christiansen et al., Mech. Dev., 51: 341–350 (1995)) and at least nine genes identified in the human (Wnt-1, -2, -3, -5A, -7A, -7B, -8B, -10B, and -11) by cDNA cloning. See, e.g., Vant Veer et al., Mol. Cell. Biol., 4: 2532–2534 (1984).
The Wnt-1 proto-oncogene (int-1) was originally identified from mammary tumors induced by mouse mammary tumor virus (MMTV) due to an insertion of viral DNA sequence. Nusse and Varmus, Cell, 31: 99–109 (1982). In adult mice, the expression level of Wnt-1 mRNA is detected only in the testis during later stages of sperm development. Wnt-1 protein is about 42 KDa and contains an amino-terminal hydrophobic region, which may function as a signal sequence for secretion (Nusse and Varmus, supra, 1992). The expression of Wnt-2/irp is detected in mouse fetal and adult tissues and its distribution does not overlap with the expression pattern for Wnt-1. Wnt-3 is associated with mouse mammary tumorigenesis. The expression of Wnt-3 in mouse embryos is detected in the neural tubes and in the limb buds. Wnt-5a transcripts are detected in the developing fore- and hind limbs at 9.5 through 14.5 days and highest levels are concentrated in apical ectoderm at the distal tip of limbs. Nusse and Varmus, supra (1992). Recently, a Wnt growth factor, termed Wnt-x, was described (WO95/17416) along with the detection of Wnt-x expression in bone tissues and in bone-derived cells. Also described was the role of Wnt-x in the maintenance of mature osteoblasts and the use of the Wnt-x growth factor as a therapeutic agent or in the development of other therapeutic agents to treat bone-related diseases.
Wnts may play a role in local cell signaling. Biochemical studies have shown that much of the secreted Wnt protein can be found associated with the cell surface or extracellular matrix rather than freely diffusible in the medium. Papkoff and Schryver, Mol. Cell. Biol., 10: 2723–2730 (1990); Bradley and Brown, EMBO J., 9: 1569–1575 (1990).
Studies of mutations in Wnt genes have indicated a role for Wnts in growth control and tissue patterning. In Drosophila, wingless (wg) encodes a Wnt-related gene (Rijsewik et al., Cell, 50: 649–657 (1987)) and wg mutations alter the pattern of embryonic ectoderm, neurogenesis, and imaginal disc outgrowth. Morata and Lawerence, Dev. Biol., 56: 227–240 (1977); Baker, Dev. Biol., 125: 96–108 (1988); Klingensmith and Nusse, Dev. Biol., 166: 396–414 (1994). In Caenorhabditis elegans, lin-44 encodes a Wnt homolog which is required for asymmetric cell divisions. Herman and Horvitz, Development, 120: 1035–1047 (1994). Knock-out mutations in mice have shown Wnts to be essential for brain development (McMahon and Bradley, Cell, 62: 1073–1085 (1990); Thomas and Cappechi, Nature, 346: 847–850 (1990)), and the outgrowth of embryonic primordia for kidney (Stark et al., Nature, 372: 679–683 (1994)), tail bud (Takada et al., Genes Dev., 8: 174–189 (1994)), and limb bud. Parr and McMahon, Nature, 374: 350–353 (1995) Overexpression of Wnts in the mammary gland can result in mammary hyperplasia (McMahon, supra (1992); Nusse and Varmus, supra (1992)), and precocious alveolar development. Bradbury et al., Dev. Biol., 170: 553–563 (1995).
Wnt-5a and Wnt-5b are expressed in the posterior and lateral mesoderm and the extraembryonic mesoderm of the day 7–8 murine embryo. Gavin et al., supra (1990). These embryonic domains contribute to the AGM region and yolk sac tissues from which multipotent hematopoietic precursors and HSCs are derived. Dzierzak and Medvinsky, Trends Genet., 11: 359–366 (1995); Zon et al., in Gluckman and Coulombel, ed., Colloque, INSERM, 235: 17–22 (1995), presented at the Joint International Workshop on Foetal and Neonatal Hematopoiesis and Mechanism of Bone Marrow Failure, Paris France, Apr. 3–6, 1995; Kanatsu and Nishikawa, Development, 122: 823–830 (1996). Wnt-5a, Wnt-10b, and other Wnts have been detected in limb buds, indicating possible roles in the development and patterning of the early bone microenvironment as shown for Wnt-7b. Gavin et al., supra (1990); Christiansen et al., Mech. Devel., 51: 341–350 (1995); Parr and McMahon, supra (1995).
The Wnt/Wg signal transduction pathway plays an important role in the biological development of the organism and has been implicated in several human cancers. This pathway also includes the tumor suppressor gene, APC. Mutations in the APC gene are associated with the development of sporadic and inherited forms of human colorectal cancer. The Wnt/Wg signal leads to the accumulation of beta-catenin/Armadillo in the cell, resulting in the formation of a bipartite transcription complex consisting of beta-catenin and a member of the lymphoid enhancer binding factor/T cell factor (LEF/TCF)HMG box transcription factor family. This complex translocates to the nucleus where it can activate expression of genes downstream of the Wnt/Wg signal, such as the engrailed and Ultrabithorax genes in Drosophila. The downstream target genes of Wnt-1 signaling in vertebrates that presumably function in tumorigenesis, however, are currently unknown.
For a most recent review on Wnt, see Cadigan and Nusse, Genes & Dev., 11: 3286–3305 (1997).
There is a need to elucidate the further members of the above families, including cell-surface molecules that may be tumor-specific antigens or proteins that serve a regulatory function in initiating the Wnt pathway of tumorigenesis. These would also include downstream components of the Wnt signaling pathway that are important to the transformed phenotype and the development of cancer.